Institutions

Useful Links

My ADS

Last Photo

Social Media

Revision

Other

Candidate benefit from our revision notes which are comprehensive and show how to tackle examination questions effectively

Results

Moreover

As a supplementary to coursework content our e-library for digitized multimedia CDs while enhance and ensure that you never missed that important concept during the normal class lessons. It is a Do it Yourself Project

KNEC

Adobe

For Best results INSTALL Adobe Flash Player Version 16 to play the interactive content in your computer. Test the link below to find out if you have Adobe Flash in your computer

Radioactivity

Background

Around the time cathode rays were
being discovered by Thomson and other scientists, Henry Becquerel
accidentally discovered another radiation. Evidence collected on the
atom suggested it could be sub-divided while others showed certain atoms
disintegrated by themselves. Becquerel discovered the phenomenon while
investigating properties of fluorescent materials as he used
photographic plates to record it.

The photographic plates were kept in
same drawer with mineral uranium while covered in opaque paper. On
developing the films they were found to be blackened or fogged.
Becquerel concluded that Uranium material must have emitted some
radiations that might have penetrated heavy paper and affected
photographic plates.

Objectives

By the end of the lesson the you
should be able to:

-Define radioactive decay and
half-life

-Describe the types of radioactive
emissions in neutral radioactivity

-Explain the detection of
radioactive emissions

-Define nuclear fission and fusion

-Write balanced nuclear equations

-Explain the dangers of radioactive
emissions

-State the applications of
radioactivity

-Solve numerical problems involving half-life.

Introduction

An atom consists of a central
nucleus having protons and neutrons called nucleons with electrons
orbiting around the nucleus. The sum of protons and neutrons is called
the atomic mass and the number of protons called the atomic number. All
natural elements with atomic numbers greater than 83 are radioactive.
However, there are a few isotopes of elements with atomic number less
than 83 were discovered to be radioactive. If the ratio of neutrons to
protons is more than 1 (one) the nucleus is usually unstable. Play the
animation below to observe a visualization of an atom with protons (+)
and neutrons while electrons, e, are orbiting around the nucleus.

Definition of radioactivity

Due to the imbalance between
neutrons and protons in the nucleus, there is instability. To achieve
stability the nucleus will tend to break (disintegrate) with emission of
energy and particles. This disintegration of nucleus is known as
Radioactivity. Click on the play button of the animation below to
observe this.

Observations

Disintegration is likely to
continue further as long as the resultant nuclei are still unstable.
Therefore, Radioactivity is the spontaneous and random disintegration of
an unstable nuclide (an atomic nucleus with a specific number of protons
and neutrons) with the emission of particles and rays.

Radioactive decay

Radioactive decay is a spontaneous
and random process in which one cannot predict the nuclide that will
disintegrate next and at what instant. To visualize this, play the
animation presented below.

Half - life

There is a time period associated
with decay of a radioactive substance when the original value reduces to
a half. The length of time during which, half of the original number of
atoms of a radioactive substance/nuclei decays is known as half-life.
Different nuclides have different half-lifes. For example, the half-life
of radium is 1600 years. This means that 2g of radium will take 1600
years to decay to 1g, similarly 1g of radium will take the same period
(1600 years) to decay to 1/2g.
The animation below shows how determination of half - life can be done,
click on its play button and make your observations.

Types of radiations

There are three types of radiations
that can be emitted during a radioactive decay. These are: alpha (A)
beta (B) and gamma (G)
radiations.

Alpha Particle

Beta Particle

Gamma rays

Gamma rays is energy emitted in
form of electromagnetic radiation. They have neither mass nor charge.
The main difference between X-rays and G-rays
is that G-rays originate from energy
changes in the nucleus of atoms while X-rays originate from energy
changes associated with the electron structure of atoms.

Detection of radioactive emissions

Photographic emulsions

All the three emissions (A,b
and G) affect photographic emulsions
or plate. They darken or blacken photographic films. The emission's
effect is observed when such plate is developed. Play the animation
below to observe how this takes place.

Cloud Chamber

Common types of cloud chambers are
expansion and diffusion cloud chambers. Click on the play button of the
animation below to observe how it works.

Explanation

When air is cooled until the vapor
it contains reaches saturation, it can be cooled further without
condensing until it reaches super-saturation. Dust should not be present
since it would act as centre of condensation. The radioactive emissions
ionize molecules in a cloud chamber to different degrees depending on
the type of emission.

The tracks obtained vary according
to the type of radiation.

(i) Alpha particles cause heavy
ionization, rapidly losing energy hence the tracks will have a short
range. Because of their larger mass they do not change their path in air
and as they pass, they cause more ionization on their path by knocking
off many electrons.

(ii) Tracks formed by beta
particles are thin and irregular in direction. This is because
beta-particles are lighter and faster hence cause less ionization of air
molecules. Also the particles are repelled by electrons of atoms in
their path.

It is a type of ionization chamber.
To visualize how this device works, play the animation below by clicking
on its play button.

Observation
When there is no source in front of the tube the scale records
background radiation which occurs naturally. An increase in the scale
reading when radioactive source is introduced is noted.Explanation

When the source is placed in front
of the window, emitted radiations or particles enter the tube through
mica window and ionize Argon gas. The negative ions move towards the
anode while positive ones towards the wall or cathode. These ions
collide with other gas molecules causing further ionization. This
avalanche effect causes a pulse of voltage corresponding to current
flowing and it is registered on the scale. An amplifier can be used to
produce audible clicks through a speaker. It can also be used to amplify
small currents from B-particles and
G-rays emissions in the scale.
Bromine gas is used as a quencher to absorb secondary electrons which
could ionize molecules and also prevents sparking.

Spark Counter

It consists of wire gauze placed a
few millimeters from a thin wire which has an adjustable voltage from an
E.H.T source. Play the video below to observe how it works.

Explanation

When source of emission(A-particles)
is brought near the wire gauze, air in its neighborhood is ionized and
ions make the gap between the gauze and wire conduct more easily. The
positively charged ions will flow towards the wire gauze causing flow of
current which produces the sparks seen. The Counter is more sensitive to
A-particles than
B-particles or
G-rays due to their lower ionization
power.

Cloud Chamber

Common types of cloud chambers are
expansion and diffusion cloud chambers. Click on the play button of the
animation below to observe how it works.

Explanation

When air is cooled until the vapor
it contains reaches saturation, it can be cooled further without
condensing until it reaches super-saturation. Dust should not be present
since it would act as centre of condensation. The radioactive emissions
ionize molecules in a cloud chamber to different degrees depending on
the type of emission.

The tracks obtained vary according
to the type of radiation.

(i) Alpha particles cause heavy
ionization, rapidly losing energy hence the tracks will have a short
range. Because of their larger mass they do not change their path in air
and as they pass, they cause more ionization on their path by knocking
off many electrons.

(ii) Tracks formed by beta
particles are thin and irregular in direction. This is because
beta-particles are lighter and faster hence cause less ionization of air
molecules. Also the particles are repelled by electrons of atoms in
their path.

When air is cooled until the vapor it contains
reaches saturation, it can be cooled further without condensing until it
reaches super-saturation. Dust should not be present since it would act
as centre of condensation. The radioactive emissions ionize molecules in
a cloud chamber to different degrees depending on the type of emission.
Common types of cloud chambers are expansion and diffusion cloud
chambers. In both types saturated vapor of either water or alcohol is
made to condense on air ions caused by the emissions producing whitish
drops of tiny liquid droplets to show tracks when illuminated. To
visualize this, Click on the play button of the animation below to
observe this.

Explanation:

The tracks obtained vary according to the type of
radiation.

(i) Alpha particles cause heavy ionization, rapidly
losing energy hence the tracks will have a short range. Because of their
larger mass they do not change their path in air and as they pass, they
cause more ionization on their path by knocking off many electrons.

(ii) Tracks formed by beta particles are thin and
irregular in direction. This is because β-particles are lighter and
faster hence cause less ionization of air molecules. Also the particles
are repelled by electrons of atoms in their path.

It is used to measure the rate of
decay or activity of a sample element and works on similar principles as
a gold-leaf electroscope with a specially designed leaf system. Play the
animation below and observe what happens.

Observations
The Leaf falls and rises repeatedly when E.H.T. is on.Explanation

Radiations from the source ionize
the air in the chamber. Due to the high electric field between central
electrode and the walls of the chamber, positive ions move towards the
chamber wall which is negative while negative ions towards the central
electrode causing the leaf to diverge and touch the side electrode. Ions
of opposite charge on the central electrode through the leaf causes
discharge and leaf falls back. The process is repeated as air in the
chamber is continually ionized, while the leaf pulses or beats at a rate
depending on value of ionization current which depends on activity.

d. The Geiger-Muller tube

It is a type of ionization
chamber. To visualize how this device works, play the animation below by
clicking on its play button.

Observation
When there is no source in front of the tube the scale records
background radiation which occurs naturally. An increase is the scale
reading when radioactive source is introduced is noted.Explanation

When the source is placed in front
of the window, emitted radiations or particles enter the tube through
mica window and ionize Argon gas. The negative ions move towards the
anode while positive ones towards the wall or cathode. These ions
collide with other gas molecules causing further ionization. This
avalanche effect causes a pulse of voltage corresponding to current
flowing through R and registered on the scale. An amplifier can be used
to produce audible clicks through a speaker. It can also be used to
amplify small currents from B-particles
and G-rays emissions in the scale.
Bromine gas is used as a quencher to absorb secondary electrons which
could ionize molecules and also prevents sparking.

e. Spark Counter

It consists of wire gauze
placed a few millimeters from a thin wire which has an adjustable
voltage from an E.H.T source. Play the video below to observe how it
works.

Explanation

When source of emission
(α-particles) is brought near the wire gauze, air in its neighborhood is
ionized and ions make the gap between the gauze and wire conduct more
easily. The positively charged ions will flow towards the wire gauze
causing flow of current which produces the sparks seen. The Counter is
more sensitive to α-particles than β-particles or γ-rays due to their
lower ionization.

Background radiation

In the absence of a radiation
source, a GM tube records a background count due to the following:

(i) Cosmic rays which enter the
atmosphere from outer space. They produce radioactive nuclides by
collision with atoms in the atmosphere

(ii) Radiations from materials in
the Earth's crust

(iii) Radiations from 'fall out'
atomic bomb tests

(iv) Radioactivity in our own
bodies

(v) Impurities with radioactive
substances present in apparatus and surrounding.

This count rate should always be
recorded before hand and subtracted from subsequent readings to get the
correct count rate.

Nuclear fission

Nuclear fission is the splitting of
a nucleus of a radioactive element due to bombardment with a neutron.
For example Uranium-235 is bombardment with a neutron and it becomes
Uranium-236 which is more active. The Uranium-236 then splits into
Barium-144 and Krypton-90 with production of more neutrons and energy.
The emitted neutrons may encounter other Uranium nuclides resulting in
more splitting with further release of energy. Play the animation below
to observe what happens when a moving neutron knocks a Uranium nuclide.

Explanation

The produced neutrons are fission
neutrons. The energy produced is called nuclear energy and the reaction
resulting with further bombardments is referred to as a chain reaction
which produces a lot of energy. Such uncontrolled reaction may result to
an explosion.

Nuclear Fusion

The fusing or combining of lighter
nuclides to form a heavier one is called nuclear fusion. This is
accompanied by enormous energy production. An example of nuclear fusion
is formation of alpha particles when two heavy hydrogen isotopes fuse.
The animation below shows two heavy isotope nuclides combining. Click on
the play button and make your observations.

Nuclear equations

In the same way if a nuclide
undergoes B-decay the atomic number
increases by 1 but there is no change in the mass number. This leads to
an isotope of same nuclide as shown in the illustration below. During
A and B-
decay, G-rays are produced in form
of energy. Note that the production of gamma rays does not affect the
mass or atomic numbers of the nuclide since they are not particulate. It
is important to note that during B-
decay the number of protons increases and occurs mostly when neutrons
are more than protons in the nucleus as in the illustration below. On
the other hand if a nuclide has excess protons it emits alpha particles
thus reducing the atomic number by 2 and mass number by 4. Therefore the
General formulae is given in the Illustration below.

Hazards of radioactivity

When the human body is exposed to
radiation, the effect of the radiation can be hazardous because of the
penetration and ionizing effect of the emissions on the cells. Gamma
rays present the main radiation hazard. This is because they penetrate
deeply into the body, causing damage to body cells and tissues. This may
lead to skin burns, blisters and sores, delayed effects such as cancer,
leukemia and hereditary defects. In 1945 during the World War II, atomic
bombs were dropped at Hiroshima and Nagasaki resulting to instant
widespread destruction felt due to the blast. Some of the damage caused
by the emitted radiation became evident within days. other devastating
effects became evident much later. The most recent accident was the
Chernobyl disaster in Ukrainian republic of the USSR on April 26, 1986.
The disaster occurred at the Chernobyl nuclear power plant that produced
plume of radioactive debris that drifted over parts of the Western USSR,
Eastern Europe, and Scandinavia. Animals feeding on the infected grass
had to be destroyed so that their products do not reach people in other
areas. It is important to note that, the harm caused by radioactive
substance is likely to take a long time because they decay slowly due to
some having long half-lives.

Precautions

Due to the hazardous nature of
radioactive substances, schools in Kenya have been prohibited from
storing them. However, the following measures are recommended as
precautions when handling radioactive substances:

1. Radioactive elements should
never be handled with bare hands but with forceps or well protected
tongs. Click on the play button to observe how this is done.

2. For the safety of the users,
radioactive materials should be kept in thick Lead boxes.

3. Persons using or working with
the radioactive sources should avoid long exposure times and be checked
regularly by a doctor for safety. A badge with photographic plate which
can be developed is used to show the amount of exposure every day.

Applications of radioactivity

Though radioactivity is hazardous
it has uses that are beneficial industrially, medically, agriculturally
and in carbon dating.

Detecting defects and bubbles in metals

The source of radioactive radiation (preferably gamma-rays) is put on
one side of a piece of forged metal while a photographic film is placed
on the other end. Play the animation below and make your observations.

Observation

When the film is developed we see the equivalent of an X-ray picture
of metal. Bubbles and defects inside the metal can be clearly detected.

b. Radioactive tracers

Radioactive tracers are used to
detect leaks in underground pipes. The tracer is fed into the pipe and
then a Geiger Muller (GM) tube is run above ground along the pipeline to
detect any increase in the radiation level and hence the leaking spot.
Play the animation below to observe how radioactivity helps in detecting
leaking spots in pipes.

c.Determining the thickness of paper

In industries which manufacture
paper and plastics, radioactive radiations can be used to determine
thickness. If a beta source is placed on one side of the paper and a GM
tube on the other side, the count-rate will be a measure of the
thickness of the paper. Click on the play button to observe how
radioactive materials can be used to control the thickness a sheet of
paper.

d. Control of static electricity

In textile industry, the presence
of static charges can be a nuisance since they can attract dust and even
cause fire. When a radioactive element is placed in such industries, the
radiations emitted will ionize air and the ions formed will attract the
static charge. This will neutralize the charges and hence solving the
problem due to static charges to a great extent.

e. Medical uses

Gamma rays, like X-rays, are used
in the treatment of cancerous body growths. They kill cancerous cells
when the tumor is subjected to them. Gamma rays are also used in
sterilization of medical equipment. To determine the position of a blood
clot in the body, a patient swallows a small amount of radioactive
sodium. After a while, the radioactive sodium flows in the bloodstream
to all parts of the body. The radioactive sodium stops flowing at the
place where a blood clot develops in a blood vessel. A detector is then
used to find out where the blood flow stops. Click "next" to view a
visualisation on this.

Click on the play button of the
animation below to observe these three uses.

f. Agricultural uses

The movement of traces of a weak
radioisotope introduced into an organism can be monitored using a
radiation detector. In agriculture, this method is applied to study the
plant uptake of fertilizers and other chemicals. Sometimes gamma
radiation is used to prolong the shelf-life of pre-packaged foods. Gamma
rays are used to kill bacteria present in food to reduce the risk of
food poisoning. Play the animation below to observe how some of these
things can be done.

g. Carbon dating

Living organisms take in small
quantities of radioactive carbon-14 in addition to the ordinary
carbon-12. The ratio of carbon-12 to carbon-14 in the organisms remains
fairly constant. When the organisms die, there is no more intake of
carbon. The ratio of carbon-14 to carbon-12 therefore changes due to the
decay of carbon 14. The new ratio is then used to determine the age of
the fossil.

Radioactivity

e-Content

Buy e-Content Digital CD covers all the topics for a particular class per year. One CDs costs 1200/-

click to play video

Purchase Online and have the CD sent to your nearest Parcel Service. Pay the amount to Patrick 0721806317 by M-PESA then provide your address for delivery of the Parcel.. Ask for clarification if in doubt,

Radioactivity

Candidate benefit from our quick revision booklets which are comprehensive and how to tackle examination question methods

We have an enourmous data quiz bank of past papers ranging from 1995 - 2017

KCSE ONLINE WEBSITE provide KCSE, KCPE and MOCK Past Papers which play a great role in students� performance in the KCSE examination. KCSE mock past papers serves as a good motivation as well as revision material for the major exam the Kenya certificate of secondary education (KCSE). Choosing the KCSE mock examination revision material saves you a lot of time spent during revision for KCSE . Choosing the KCSE mock examination revision material saves you a lot of time spent during revision for KCSE. It is also cost effective

MOCK Past Papers

As a student, you will have access to the most important resources that can help you understand what is required for you to sit and pass your KCSE examination and proceed to secondary school or gain entry to University admission respectively.

KCSE ONLINE

KCSE ONLINE WEBSITE provide KCSE, KCPE and MOCK Past Papers which play a great role in students� performance in the KCSE examination.

Choosing the KCSE mock examination revision material saves you a lot of time spent during revision for KCSE. It is also cost effective

Ask for clarification if in doubt, vitae dignissim est posuere id.

Radioactivity

sit amet congue Mock Past Papers, give you an actual exam situation in readiness for your forthcoming national examination from the Kenya National Examination Council KNEC

Choosing the KCSE mock examination revision material saves you a lot of time spent during revision for KCSE. It is also cost effective sapien.

Choosing the KCSE mock examination revision material saves you a lot of time spent during revision for KCSE. It is also cost effective sapien.

Radioactivity

As a supplementary to coursework content our e-library for digitized multimedia CDs while enhance and ensure that you never missed that important concept during the normal class lessons. It is a Do it Yourself Project..

Candidates who would want their papers remarked should request for the same within a month after release of the results. Those who will miss out on their results are advised to check with their respective school heads and not with the examination council

For Best results INSTALL Adobe Flash Player Version 16 to play the interactive content in your computer. Test the link below to find out if you have Adobe Flash in your computer.